The speed rusher traditionally (not allways) plays on the right side on deffense to attack the QB's blind side. LT's are there to keep the QB's vision open and not worry about what they cannot see. LT's are allways going to be the most important (for a right handed thrower).

But nowadays, the LE is also turning into a speed rusher and because many QB's roll out in different direction more than ever, the RT is a big deal compared to 10 years ago.

Colombo is right on the line between average and slightly above it.
He doesn't have much upside, and will never have very good leg drive.
That being said, he does have a nasty demeanor on the field, and isn't going to hurt you much.
He won't get much push in the ground game, and he is pretty decent in pass protection.
He's probably not worth the money you gave him.